A rapidly developing area of wireless networks is mobile ad hoc networks. Physically, a mobile ad hoc network includes a number of geographically-distributed, potentially mobile nodes wirelessly connected by one or more radio frequency channels. Compared with other type of networks, such as cellular networks or satellite networks, the most distinctive feature of mobile ad hoc networks is the lack of any fixed infrastructure. A pure mobile ad hoc network is formed of mobile nodes only, and a network is created on the fly as the nodes transmit to or receive from other nodes. Node movement patterns may be anywhere from continuous to start-stop type patterns. The network does not in general depend on a particular node and dynamically adjusts as some nodes join or others leave the network.
An ad hoc network can be quickly deployed and provide much needed communications. Ad hoc networks will allow people to exchange data in the field or in a class room without using any network structure except the one they create by simply turning on their computers or PDAs, for example.
New applications for mobile ad hoc networks will continue to emerge and become an important part of the communication structure. Due to the lack of a fixed infrastructure, nodes must self-organize and reconfigure as they move, join or leave the network. All nodes could potentially be functionally identical and there may not be any natural hierarchy or central controller in the network. Many network-controlling functions are distributed among the nodes. Nodes are often powered by batteries and have limited communication and computation capabilities. The bandwidth of the system is usually limited. The distance between two nodes often exceeds the radio transmission range, and a transmission has to be relayed by other nodes before reaching its destination. Consequently, a network has a multihop topology, and this topology changes as the nodes move around.
The Mobile Ad-Hoc Networks (MANET) working group of the Internet Engineering Task Force (IETF) has been actively evaluating and standardizing routing, including multicasting, protocols. Because the network topology changes arbitrarily as the nodes move, information is subject to becoming obsolete, and different nodes often have different views of the network, both in time (information may be outdated at some nodes but current at others) and in space (a node may only know the network topology in its neighborhood usually not far away from itself).
A routing protocol needs to adapt to frequent topology changes and with less accurate information. Because of these unique requirements, routing in these networks is very different from others. Gathering fresh information about the entire network is often costly and impractical. Many routing protocols are reactive (on-demand) protocols: they collect routing information only when necessary and to destinations they need routes to, and do not generally maintain unused routes after some period of time. This way the routing overhead is greatly reduced compared to proactive protocols which maintain routes to all destinations at periodic time intervals. It is important for a protocol to be adaptive. Ad Hoc on Demand Distance Vector (AODV), Dynamic Source Routing (DSR) and Temporally Ordered Routing Algorithm (TORA) are representative of on-demand routing protocols presented at the MANET working group.
Examples of other various routing protocols include Destination-Sequenced Distance Vector (DSDV) routing which is disclosed in U.S. Pat. No. 5,412,654 to Perkins, and Zone Routing Protocol (ZRP) which is disclosed in U.S. Pat. No. 6,304,556 to Haas. ZRP is a hybrid protocol using both proactive and reactive approaches based upon distance from a source node.
These conventional routing protocols use a best effort approach in selecting a route from the source node to the destination node. Typically, the number of hops is the main criteria (metric) in such a best effort approach. In other words, the route with the least amount of hops is selected as the transmission route.
Existing communication node advertisement and communication node neighbor discovery approaches including those for ad hoc networks, only use network-condition-independent mechanisms such as constant transmit rate or random transmit rate “hello” messages from nodes to announce, or advertise, their presence. These transmitted announcements are called “beacons” and conventional approaches do not endow these beacons with any degree of intelligence. Other nodes may detect these beacons and either form a network from scratch, add the newly-detected node to the existing network, or disallow further communications to this newly-detected node.